Technology and real estate investments led deal-making by sovereign funds in 2016 and the first half of 2017 according to a report published on Wednesday, with six funds accounting for over 70 percent of transactions.

Sovereign wealth funds (SWFs), which reinvest surpluses from commodity exports or trade, have about $7.5 trillion under management globally.

In recent years they have increased their exposure to unlisted assets in pursuit of higher returns, although some funds are now hitting upper limits on their allocations.

The IE Business School's latest annual Sovereign Wealth Funds Report showed deal-making remains concentrated among a handful of key players, because it requires large specialist teams to identify, assess and execute transactions.

"This expertise in private markets and assets required to invest abroad and deploy large sums of capital directly is an entry barrier for other SWFs," said Javier Capape, co-author of the report and a director at the IE Business School's Sovereign Wealth Lab.

Temasek, a Singapore state-owned investment company, accounted for 101 deals, or 30 percent of the total over the 18-month period. Singapore's SWF GIC managed 63 deals, or 19 percent.

Together with Abu Dhabi Investment Authority, Qatar Investment Authority, the Ireland Strategic Investment Fund and China Investment Corporation (CIC), they accounted for over 70 percent of the acquisition count.

Technology was the most popular sector, accounting for 26.1 percent of total transactions in the first half of 2017, up from 24.3 percent in 2016.

More SWFs are sinking money into tech start-ups in an attempt to protect their holdings in mature sectors from new companies such as Airbnb and Uber. Artificial intelligence and virtual reality have also attracted interest.

Real estate accounted for 23.9 percent of deals in the first half of 2017, up from 21.5 percent in 2016.

CIC's acquisition of pan-European warehouse group Logicor was the biggest deal in the first half of 2017, worth $13.8 billion.

Logistics companies are considered well-placed to benefit from the growth of companies like Amazon, which use massive warehouses as distribution hubs. Student housing and high- quality office blocks also remained popular with SWFs.

The United States, India, Singapore, China, Australia, and Britain were key destinations.

Capape said it was too early to say whether Britain's vote to leave the European Union had had an impact on its appeal to SWFs: "They may be benefiting from a low pound. We can't say it's a big drop in investments after Brexit."

He noted an uptick in interest in emerging-market infrastructure, which soared from 3 percent of direct investment in infrastructure in 2012 to nearly 30 percent in 2016.

At the same time, infrastructure's share of total foreign direct investment dollars spent rose from 12 percent in 2015 to 20 percent in 2016.

Developed markets, with exceptions such as Australia and Britain, have failed to satisfy SWF demand for infrastructure and utility plays.

With President Donald Trump releasing his long-awaited infrastructure plan on Monday, the United States could offer fresh opportunities.

But Capape said some funds might run into opposition on national security grounds. The Committee on Foreign Investment in the United States, which reviews acquisitions by foreign entities for potential national security risks, has become more risk-averse under Trump.

"The criticism that comes from some SWFs when investing in developed markets is that this definition of national security is very loose and it may be used to defend against important assets being controlled by foreigners," he said.